U.S. patent number 5,722,899 [Application Number 08/767,348] was granted by the patent office on 1998-03-03 for method for making a matched set of golf clubs utilizing frequency conversion values.
This patent grant is currently assigned to Harrison Sports, Inc.. Invention is credited to Michael H. L. Cheng.
United States Patent |
5,722,899 |
Cheng |
March 3, 1998 |
Method for making a matched set of golf clubs utilizing frequency
conversion values
Abstract
Methods of making a set of golf clubs and shafts that are
matched according to vibration frequency are disclosed. The methods
may include a random selection of shafts from a stock of raw
shafts, wherein the vibration frequency of each shaft is determined
and then each shaft is assigned a club head number. By determining
conversion values based on desired and actual club head weights for
each shaft and by determining a value between a desired and
measured frequency of each shaft, a total frequency conversion
value may be obtained. The total frequency conversion value may
then be used to determine an amount to trim each shaft and thereby
linearly match each shaft in the set based on vibration frequency
and an increase in club head number.
Inventors: |
Cheng; Michael H. L. (Simi
Valley, CA) |
Assignee: |
Harrison Sports, Inc.
(N/A)
|
Family
ID: |
25079204 |
Appl.
No.: |
08/767,348 |
Filed: |
December 18, 1996 |
Current U.S.
Class: |
473/289;
473/290 |
Current CPC
Class: |
A63B
60/00 (20151001); A63B 53/00 (20130101); A63B
53/005 (20200801) |
Current International
Class: |
A63B
53/00 (20060101); A63B 053/00 (); A63B
053/10 () |
Field of
Search: |
;473/289,287,290,291 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Passaniti; Sebastiano
Assistant Examiner: Blau; Stephen L.
Attorney, Agent or Firm: Oppenheimer Poms Smith
Claims
What is claimed is:
1. A method of making a matched set of golf clubs comprising the
steps of:
randomly selecting a plurality of shafts from a stock of raw
shafts;
determining the weighted vibration frequency of each of the
plurality of shafts;
assigning sequential club head numbers to each shaft in the order
of the frequency of each shaft, starting with the lowest club head
number being assigned to the shaft having the lowest vibration
frequency;
selecting a club head for each respective shaft;
determining the actual weight of each club head;
selecting a desired club head weight for each shaft;
determining a weight difference conversion value to adjust the
determined vibration frequency of each shaft based on the desired
club head weight;
determining an overage conversion value to adjust the determined
vibration frequency of each shaft based on the actual weight of a
selected club head in excess of the desired club head weight;
determining for each shaft a total frequency conversion value
comprising the addition of (a) said weight difference conversion
value, (b) the overage conversion value, and (3) the difference
between the desired vibration frequency (minuend) and the
determined vibration frequency (subtrahend);
determining for each shaft a tip trim amount based on the total
frequency conversion value; and
trimming the tip of each shaft by said determined tip trim
amount.
2. A method in accordance with claim 1, wherein said step of
determining a weight difference conversion value is obtained by
frequency testing a representative shaft to obtain conversion data
showing the relationship between increasing club head weight to
decreasing vibration frequency for said representative shaft, and
then by correlating said desired club head weight to a decrease in
vibration frequency from said conversion data to thereby obtain
said weight difference conversion value.
3. A method in accordance with claim 2, wherein said step of
determining an overage conversion value includes measuring the
actual weight of a selected club head, determining any excess in
the weight of said selected club head from said desired club head
weight, and correlating said excess to a decrease in vibration
frequency from said conversion data to thereby obtain said overage
conversion value.
4. A method in accordance with claim 3, wherein said step of
determining a tip trim amount includes formulating for a
representative shaft trim conversion data setting forth a
relationship between tip trim amount and a resulting increase in
vibration frequency, and correlating said total frequency
conversion value with said trim conversion data to obtain said tip
trim amount.
5. The method of claim 4 wherein said trim conversion data is
formulated by using a frequency analyzer which clamps the shaft
near its butt and incrementally moving the shaft into the analyzer
for each test to simulate shorter shafts.
6. A method in accordance with claim 1, further comprising the
steps of supplementing the actual weight of a selected club head
which is less than said desired club head weight by providing
supplemental weight which is substantially equal to the difference
between said selected club head weight and said desired club head
weight.
7. A set of golf clubs which are produced by utilizing a method
comprising the steps of:
randomly selecting a plurality of shafts from a stock of raw
shafts;
determining the weighted vibration frequency of each of the
plurality of shafts;
assigning sequential club head numbers to each shaft in the order
of the frequency of each shaft, starting with the lowest club head
number being assigned to the shaft having the lowest vibration
frequency;
selecting a club head for each respective shaft;
determining the actual weight of each club head;
selecting a desired club head weight for each shaft;
determining a weight difference conversion value to adjust the
determined vibration frequency of each shaft based on the desired
club head weight;
determining an overage conversion value to adjust the determined
vibration frequency of each shaft based on the actual weight of a
selected club head in excess of the desired club head weight;
determining for each shaft a total frequency conversion value
comprising the addition of (a) said weight difference conversion
value, (b) the overage conversion value, and (c) the difference
between the desired vibration frequency (minuend) and the
determined vibration frequency (subtrahend);
determining for each shaft a tip trim amount based on the total
frequency conversion value; and
trimming the tip of each shaft by said determined tip trim amount.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for making a set of golf
clubs wherein each club is matched to the set according to certain
club characteristics. The present invention particularly relates to
a method for making a set of golf clubs wherein each club is
matched to the set according to vibration frequency.
2. Prior Art and Related Information
Golf is a demanding game that challenges the ability of each
player. As is a common occurrence in most sports, creative
individuals have attempted to enhance the performance of golfers by
improving the sports equipment they use. In the case of golf, a
typical pursuit of golf club manufacturers is to improve the feel
and control of the golf clubs.
Since golf is played with a number of golf clubs, each of which is
carefully selected for a given type of playing circumstance, any
variation in the feel and control from one club to the next is
likely to affect the golfer's performance. For example, in a
typical set of golf clubs which includes three wood drivers and
eight irons, the drivers are used to achieve long distance travel
of the golf ball and the irons are used to accurately place the
golf ball as close to the pin as possible after a long drive. The
drivers typically have long shafts, while the irons decrease in
shaft length as the head number increases. Moreover, with
increasing head number, the club head is configured to give the
golf ball more loft and less distance. It is therefore evident that
a golfer needs to experience consistent feel and control from one
club to the next to ensure consistent impact and proper placement
of the golf ball during a round of golf.
One way of advancing the goal of having a consistent feel and
control from one club to the next within a set of clubs is to
ensure that when the set of clubs is created, each club is matched
to the next club by a certain physical characteristic of the club
shaft. One particularly popular characteristic useful for this
purpose is the vibration frequency of the golf club shaft which
vibration frequency is typically defined as the oscillation in
cycles per minute (CPM) of a shaft when it is clamped at its butt
end in a cantilever fashion and the tip of the shaft has been
pulled and released. Specifically, many golfers have found that a
greater consistency in feel and control within a set of golf clubs
is obtained when the vibration frequency of each shaft increases
with increasing club head number. It is sometimes preferred that
the vibration frequency increases linearly with increasing club
head number and sometimes it is preferred that vibration frequency
increase linearly with decreasing shaft length (i.e., shaft length
decreases with increasing club head number).
A number of methods for creating a matched set of golf clubs
according to vibration frequency have been formulated in the past.
U.S. Pat. Nos. 4,070,022 and 4,122,593 to Braly; U.S. Pat. No.
5,163,681 to Hodgetts; U.S. Pat. No. 4,128,242 to Elkins, Jr.; U.S.
Pat. No. 4,555,112 to Masghati; and U.S. Pat. No. 4,900,025 to
Suganuma each relate to such methods. However, known methods for
such frequency matching often include such highly selective
criterion in choosing a particular shaft from existing stock that
stock is potentially wasted or must be deemed scrap. In addition,
the selection process proves so labor intensive that costs of
manufacture are often prohibitively high. Finally, the time
required for such a selection process inevitably lengthens the
manufacturing process.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention
to provide a method of manufacturing a matched set of golf clubs
with reduced costs and reduced delays without compromising the
desired consistent feel and control among the golf clubs within the
set.
It is a further object of this invention to provide a method of
manufacturing a set of golf clubs which are matched by vibration
frequency and particularly where each club has a vibration
frequency which is linearly related to the club head number.
In accordance with the present invention, a method is provided for
making a matched set of golf clubs. The method may include the
steps of randomly selecting a plurality of raw shafts from a stock
of raw shafts and then determining the vibration frequency of each
of the plurality of shafts. The shafts are then assigned a club
head number according to the frequency of each shaft starting with
the lowest club head number being assigned to the shaft having the
lowest vibration frequency. A desired club head weight for each
shaft is selected and then a weight difference conversion value is
determined to adjust the determined vibration frequency of each
shaft based on the desired club head weight.
In the event the actual club head weight is greater than the
desired club head weight, an overage conversion value is
determined. Next, a desired frequency is selected for each club
within the set so that the vibration frequency of each club in the
set will increase linearly with increasing club head number. In
fact, because as each club head number increases, the length of
each shaft decreases, it is preferably desired that the vibration
frequency of each golf club increase linearly with decreasing golf
club shaft length.
After the desired vibration frequency has been selected, and the
determined vibration frequency has been determined by testing, the
total frequency conversion value is calculated by adding (1) the
weight conversion value, (2) the overage difference conversion
value, and (3) the number determined by subtracting the determined
vibration frequency from the desired vibration frequency. Based on
the total frequency conversion value, a tip trim amount is
determined, and the tip of the shaft is then trimmed by said tip
trim amount. After the tip is properly trimmed, the butt is also
trimmed to achieve the desired length. Because the shaft was
vibration-tested by clamping the shaft ahead of the butt, the
trimming of the butt has no effect on the shaft's vibration
frequency.
Also note that, although this process has been described with a
particular vibration frequency relationship between the shafts in a
set of clubs, this process can be performed to achieve any desired
frequency characteristic for a single golf club or a set of golf
clubs. A set of golf clubs is defined as any three or more golf
clubs with different club head numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects, features and advantages of the present invention will
be apparent to one skilled in the art from reading the following
detailed description and the following figures:
FIG. 1 is a chart listing exemplary vibration frequency values for
nine randomly selected shafts;
FIG. 2 is a chart listing data that identifies the effect of
incremental head weight differences on the vibration frequency of a
particular shaft;
FIG. 3 is a chart listing data for calculating the overage and
weight difference conversion values based on actual and desired
weights for a club head for each shaft listed in FIG. 1;
FIG. 4 is a chart listing data that identifies the effect of
trimming the tip of a shaft of FIG. 1 on its vibration
frequency;
FIG. 5 is a chart listing exemplary desired vibration frequency
values for three sets of golf clubs having relatively different
stiffnesses; and,
FIG. 6 is a chart listing data for calculating a total frequency
conversion value for each shaft and for determining the tip trim
amount necessary to create in each shaft of FIG. 1 the desired
vibration frequency.
DETAILED DESCRIPTION OF THE INVENTION
The following description describes a method for the creation of a
matched set of golf clubs wherein the vibration frequency of each
golf club in the set increases with increasing club head number. In
its preferred embodiment, the method of this invention is practiced
with graphite golf club shafts which are made by known methods of
wrapping pre-cut graphite sheets around a mandrel.
Typically, the shafts are made to include a relatively thin tip
portion, a relatively larger butt portion and an intermediate
tapered portion which joins the tip portion and the butt portion.
The use of the mandrel results in a shaft having an opening passing
through the shaft.
A conventional set of matched clubs typically includes one to three
wood drivers, eight irons, a pitching wedge, a sand wedge and a
putter. Although the method of the present invention is applicable
to the manufacture of all of these types of clubs, the description
below is directed to matching a set of irons (numbered two through
nine) and a pitching wedge. As such, the description is merely
exemplary and does not limit the utility of the invention in any
way.
In an initial step, nine different raw shafts are randomly selected
from a stock of shafts and then tested to determine the weighted
frequency of each shaft. The frequency is measured by known methods
which include securing the butt end of the shaft in place at a
stationary location and fastening a predetermined test weight at
the tip end of the shaft. The shaft is then excited and the
resulting oscillations are measured to determine the weighted
frequency (in cycles per minute or "CPM"). In a preferred
embodiment, the predetermined test weight is 235 grams for irons,
which is typically the weight of a two-iron head, and 200 grams for
woods which is typically the weight of a driver head.
Upon obtaining the frequency of the nine randomly selected raw
shafts, each shaft is then assigned a club head number (in this
case the head numbers range from a two iron through pitching wedge,
inclusive) starting with the shaft having the lowest vibration
frequency and ending with the shaft having the highest vibration
frequency. That is, the lowest frequency shaft will be assigned the
two-iron designation and the highest frequency shaft will be
assigned the pitching wedge designation. The intermediate shafts
will similarly be assigned a head number depending upon the
increasing vibration frequency of each shaft. To avoid later
confusion, each of the nine shafts should be clearly labeled with
its club head designation.
By way of example, FIG. 1 shows the measured vibration frequency
values of nine randomly selected raw shafts (left and middle
column). In addition, FIG. 1 shows the assignment of iron head
number designations (right column) starting from the shaft with the
lowest vibration frequency (shaft number eight) and ending with the
highest (shaft number nine).
The next step is to select the club heads which will be attached to
each respective shaft and to weigh each club head to determine
their actual weight.
Following the assignment of a club head designation to each shaft,
the next step is to determine the effect on vibration frequency, if
any, that the weight of the later-attached club head will have on
each shaft. This determination is needed because the vibration
frequency of the shafts were all initially measured using a typical
two-iron club head weight (235 grams) whereas the ultimate actual
club head weight, at least for the three-iron through pitching
wedge clubs, will incrementally increase from that value as head
number increases. Presently, it is customary for club heads to
increase in weight by 7 grams for each increase in club number, and
it is known that as club head weight increases, the shaft vibration
frequency will decrease.
To perform this calculation, it is first necessary to obtain weight
vs. frequency (CPM) data to show the relationship between an
increase in head weight to a reduction in shaft frequency. To
obtain this data, frequency testing of a representative shaft is
performed using incremental test weights. An example chart
containing such data is shown in FIG. 2 wherein a representative
iron graphite shaft was frequency tested using test weights of 2,
4, 6, and 7 grams.
Once weight increase vs. frequency reduction data has been
obtained, it is next necessary to equate the change in club head
weight to a decrease in shaft frequency. In that connection,
reference is made to the chart provided in FIG. 3.
In Column A, the desired weight of each club head, two-iron through
pitching wedge, is listed. The desired weights in FIG. 3 are
exemplary and will be determined by the needs of the manufacturer;
however, in this example, the desired weight of each club head
increases incrementally by seven grams from the typical 235 gram,
two-iron club head. From the data in FIG. 2, it is then
extrapolated that each seven gram increase over the 235 gram
two-iron head weight will lead to approximately a five CPM decrease
in shaft frequency. Accordingly, the needed increase in shaft
frequency for each desired club head weight is listed in Column G
of FIG. 3.
Next, it is necessary to determine the effect on shaft frequency of
the deviations in weight between the desired club head weight and
the actual club head weight for each shaft. From this information,
the overall adjustment due to club head weight to the measured
frequency can then be determined. If the actual weight is below the
desired weight, a weight pin, lead tape, lead powder, or other
supplemental means of increasing weight, will be introduced to
increase the actual weight to the desired weight. If the actual
weight is greater than the desired weight, it must then be
determined by how much the additional weight will further reduce
shaft frequency. In that connection, reference is again made to
FIGS. 2 and 3.
In Column B of FIG. 3, the actual weight of the club head that will
be attached to each shaft is listed. These weights are determined
using conventional weighing methods. If the actual weight is less
than the desired weight, an underage is thereby identified. In FIG.
3 this value is listed in Columns C and D, Column C thereby
identifies the underage in weight and Column D thereby identifies
how much supplemental weight must be added. In lieu of a weight
pin, lead powder or lead tape can be used in the conventional
manner to supplement the weight of the head. If the actual weight
is greater than the desired weight, an overage is thereby
identified. In FIG. 3, the overage is listed in Column E.
In those instances where a weight underage exists, the addition of
supplemental weight will bring the weight of the club head to the
desired weight as listed in Column A. Consequently, the only
adjustment to the frequency of the shaft will be the adjustment
required by the previously discussed incremental weight increase in
the desired club head weight for each shaft. As also previously
discussed, these adjustments are listed in Column G.
In those instances where a weight overage exists, however, an
additional frequency compensation is necessary. That additional
frequency compensation is obtained by comparing the overage with a
decrease in frequency value according to the data of the chart of
FIG. 2. The resulting overage conversion value for each shaft
having an overage in the example of FIG. 3 is listed in Column
F.
Finally, to obtain the frequency adjustment required for each shaft
due to actual club head weight, the conversion value resulting from
the incremental increase in desired club head weight and the
conversion value resulting from an actual club head weight in
excess of the desired club head weight are then added together to
arrive at an overage and weight difference conversion value. In
FIG. 3, the overage and weight difference conversion value due to
actual club head weight for each shaft is listed in Column H.
Now that the overage and weight difference conversion value is
obtained, it remains to determine the amount each shaft must be
trimmed to achieve the desired frequency for each club. A number of
preliminary steps, however, must be performed. First it is
necessary to determine the relationship between tip trimming and an
increase in shaft frequency. Next it is necessary to select the
desired frequency for each shaft that will comprise the set. Then,
the difference between the desired frequency and the actual
frequency as adjusted for club head weight must be calculated.
The increase in shaft frequency resulting from tip trimming will
depend directly upon the type of shafts being manufactured and the
material properties of such shafts. By way of example only, a
graphite shaft of the preferred embodiment has been determined to
have the tip to frequency relationship embodied by the data in FIG.
4. The first column shows the tip trim in inches and the second
column shows the resulting increase in shaft frequency in cycles
per minute.
The tip-to-frequency relationship can be determined by selecting a
representative shaft and incrementally trimming the tip and
measuring the new frequency, and thus determining the increase in
frequency resulting from the tip being trimmed. An alternative
method of determining this relationship is, rather than actually
trimming the tip of a representative shaft, to move the shaft
incrementally further into the frequency analyzer, thus simulating
a shorter shaft. This method will permit a large number of
incremental testing, avoid destruction of a shaft, and permit
testing of the actual shaft to be used in making the golf club.
As for the desired frequency for each shaft comprising the set,
FIG. 5 is a chart showing exemplary desired frequencies (in CPM)
for iron nos. 2 through 9 and a pitching wedge. For each of the
irons and for the pitching wedge, FIG. 5 further includes exemplary
frequencies for shafts of different flex designations.
Conventionally, flex designation "A" signifies a semiflexible
shaft, designation "R" signifies a regular shaft, and designation
"F" signifies a firm or stiff shaft. In FIG. 5, the frequency
increases by four CPM with each incremental increase in club head
number. It is understood, however, that the frequency values in
FIG. 5 are only samples of desired frequencies and that the desired
frequency for any particular set of clubs will depend on the needs
and criteria of the manufacturer.
As for the difference between the desired frequency and the actual
frequency as adjusted for club head weight, a comparison is first
made between the desired frequency and the frequency initially
measured for each shaft (using the predetermined weight). In that
connection, Column A of FIG. 6 lists the frequencies initially
measured in the example of FIG. 1, and Column B lists the desired
frequency for each shaft as the frequency for a "R" flex shaft (See
also FIG. 5). The difference between the actual and desired
frequencies is then calculated. This value is listed in FIG. 6 at
Column C. Added to this difference is the overage and weight
difference conversion, value, which is listed in FIG. 6 at Column D
(See also FIG. 3 at Column H) to arrive at the Total Frequency
Conversion Value in CPM between the shaft as selected from stock
and the shaft as ultimately desired. This Total Frequency
Converison Value is listed in FIG. 6 at Column E.
The Total Frequency Conversion Value as finally obtained is then
compared to the data for tip trimming which is exemplified in FIG.
4. For the preferred embodiment, the Total Frequency Conversion
Value is divided by eighteen CFM with the resulting quotient being
the amount, in inches, that the tip should be trimmed to obtain the
desired frequency. In FIG. 6, this tip trim amount is listed in
Column F.
To complete the process of manufacturing the set of frequency
matched shafts, each shaft will be trimmed by the calculated
amount, thereby resulting in a set of shafts in which the shaft
vibration frequencies have the desired relationship to club head
number. In addition, any supplemental weight necessary to adjust
the club head weight will have been added to the club head, the
club head will be attached to its assigned shaft and any other
finishing aspects of assembly as commonly practiced in the
manufacture of golf clubs will be performed.
Finally, the butt will be trimmed by the necessary amount to
achieve the desired club length for the club head number. However,
so long as the amount of butt which is removed is less than the
amount which extended beyond the clamped portion of the shaft
during the vibration testing, the vibration frequency of the shaft
will not be affected.
By following the above described steps for a random selection of
shafts from stock, it is seen that the manufacturer can easily and
efficiently obtain a frequency matched set of golf clubs and
thereby better ensure a consistent feel and control to the user
from one club to the next. This method also reduces the likelihood
of shaft stock being scrapped and reduces the labor, delay and
expense incurred in current methods.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize
that changes may be made without departing from the spirit and
scope of the invention.
* * * * *